<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">This special issue of</b> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IEEE Design&Test</i> is about benchmarking machine learning (ML) applications. A special issue on benchmarking is long overdue. The last one I can find is one I edited way back in 2000. That issue covered the ITC99 benchmarks that I put together and introduced at a special session of the 1999 International Test Conference. These were used for comparing automatic test pattern-generation (ATPG) algorithms.